Error P0104 – how to fix it?

P0104 Setting the fault code.

Electrical ground flow circuit (MAF) Irregular and abnormal output.

• Code P0104 is normally associated with codes P0100, P0101, P0102 and P0103.

What does the P0104 code mean?

P0104 is a code for mass airflow (MAF) sensor problems with inconsistent, erratic or irregular high voltage/signal output to the engine control unit (ECU).

What causes the P0104 code?

The MAF sensor has intermittent problems with high output voltage and can have several causes:

• The source of the problem is that the voltage sensor is not sending the correct output voltage required by the ECU.
• The most basic problem is that the air flow from the air filter to the MAF sensor is too erratic.
• The wiring harness or MAF sensor may be damaged or have a bad electrical connection. It may also be too close to high voltage components, especially alternators, ignition wires, etc., causing abnormal signal interference.
• The air intake system may have a major leak, such as a damaged vacuum line, a loose air intake line, loose hose clamps, or other leak in the intake system before the MAF sensor. Leaks can be cracks that open and close, depending on the engine speed and load.
• MAF sensors must operate within certain limits to send the correct signals to the ECU to properly adjust engine operation, which are compatible with other sensor outputs.

What are the symptoms of code P0104?

• The P0104 code is usually preceded by the Check Engine light on the instrument panel display.
• Normally the vehicle runs well enough to drive, but needs attention. The engine runs almost normally, but may run somewhat erratically, have less power, flame back, and an inconsistent higher than normal idle. Continuing to drive the car can cause internal engine damage.

How can a mechanic diagnose the P0104 code?

• P0104 is diagnosed using an OBD-II scanner. A qualified technician must then reset the OBD-II error codes and perform a road test of the vehicle to see if the code and engine warning light return. This can be observed by watching the live data on the scanner while driving. If the code returns, then the mechanic will need to do a thorough inspection to determine if there are electrical connectors, cables, sensor, air filter, intake and vacuum lines, loose hose clamps, and MAF problems.
• If no problems are observed, then the next step is for the technician to do a circuit test with a multimeter that has a display to show the sampling frequency and sensor range voltage readings to determine if the MAF sensor output is indeed erroneously high.

Common P0104 Code Diagnostic Errors

• The diagnostic errors are largely due to the fact that the correct procedure was not followed. First, perform the test procedure for the connector, wiring, and sensor.
• Do not buy an MAF sensor unless further testing indicates that there is no problem and that the sensor is defective.
• Before buying an MAF sensor, try cleaning it with a specialized spray cleaner, such as CRC 05110, made for MAF sensors, as these often have significant carbon buildup from the emission system, especially at idle.
• The air intake system can have simple causes such as loose clamps, air hoses or vacuum lines, so a thorough inspection is necessary before purchasing an expensive MAF unit.

How serious is the code P0104?

• The P0104 code will not prevent you from driving unless the leak is very large.
• A problem with the MAF sensor can cause excessive fuel consumption, malfunction and starting difficulty under certain circumstances, and even damage the engine if the vehicle is still being driven, but it is better to diagnose the problem more accurately.
• In occasional cases, the code can be reset and the vehicle will run normally without the engine warning light or code reappearing.
• Often, if the engine warning light comes on immediately after starting, and the OBD-II system can be reset and the vehicle will operate normally.

What repairs can fix the P0104 code?

The most common fixes to repair the P0104 code are as follows:

1. Check the code with a scanner. Reset the trouble codes with the OBD-II scanner and perform a road test.
2. If the P0104 code and/or the engine warning light return, perform the test procedure.
3. Check the electrical connector to make sure it is connected. Disconnect and reinstall to ensure a new electrical connection.
4. Carefully inspect the connector for frayed or damaged wires. If necessary, repair or replace before proceeding.
5. Check the air intake system for vacuum leaks, loose hoses, and clamps on the intake, especially on older cars.
6. Replace the MAF sensor if no other problems are found.

Additional notes on code P0104

Many vehicles with mileage over 100,000 have temporary sensor problems, which often occur during starting or prolonged charging of the drivetrain.

If the engine warning light comes on and the vehicle appears to be operating normally, the OBD-II system can be reset with a scanner and the problem may not recur. Therefore, it is important to check the malfunction and reset it before repairing it.